1. Field of the Invention
The present invention relates to a photograph image-processing method and the device thereof, which adjusts color balance of R (red),. G (green), and B (blue) (hereinafter called “RGB”) so that natural color can be reproduced with respect to color image data obtained by reading photographic films, for example, negative films, etc.
2. Description of the Related Art
In conventional photograph printers, as a photograph image-processing method to print images recorded on negative film onto photographic printing paper, photosensitive material, in good color shades, an LATD (Large Area Transmittance Density) exposure system based on the Evans' theory is known. This exposure system is a method to adjust each exposure rate of RGB in such a manner that the RGB integrated light that penetrates negative film is reproduced in gray when any deviation is observed in color, in accordance with the Evans' theory that when colors of the whole negative film are mixed, the color of an average outdoor photographic subject gets closer to gray. Specifically, the negative film is irradiated with light, the transmitted light is read by an image pickup device to create RGB color image data, the mean value of the color image data is calculated and derived for every RGB of each pixel, and in analog type photograph printers, a photochromic filter is adjusted to expose the photographic printing paper, and in digital type photograph printers, the exposure rates from relevant light sources of RGB are adjusted, respectively, so that each mean value of RGB achieves the specified value that corresponds to gray, respectively.
According to the conventional photograph image-processing method described above, there was a problem that the negative film is overcorrected due to color deviations of a photographic subject (person, background) and a photographic print all the more difficult to see is outputted. For example, in the case of a scene in which a person is photographed against a background of the grass, the area of the grass is finished in gray, while in the area of the person, magenta which is a complementary color of the grass strongly appears. This kind of condition is called color failure, and as the measures, a method for removing the high chromatic pixel in the LATD exposure method or a method to find conditional mean values weighted by chroma, and others are proposed in Japanese Unexamined Patent Publication No. 2000-330221.
However, according to the above-mentioned method, in the case of a scene with large color deviation, the number of pixels used for calculation becomes extremely small, resulting in a tendency of short stability, and even with small weighting, if the number of pixels that correspond to this is large, the print results are not a little affected. Furthermore, since the threshold values to remove the high chroma pixels or weighting conditions by chroma were determined empirically, they were not always infallible and there was a room for further improvement.